If your having trouble with Parts Source, there is always Altrom on Exeter Road in London. Also APC on Adelaide (I always deal with them and they seem to be good), NAPA on Oxford, and Carquest on First St.

I just remembered also that Corey's Auto Wreckers on Gore Road has an rolled over e39 sitting in the back that may have a good rad. Only thing is that is maybe expensive to buy it, they usually charge a good buck for stuff. Here's the number anyways (519) 455-9040